This is one of the GPS units we use in our chase vehicles (the other
being the newer AvMap G5). We use the AvMap because it is an APRS
capable unit,
meaning it connects directly to our Kenwood mobile radio via the
included cable. Both the car's position and the balloon's current
position are shown on the LCDisplay. It runs off a standard
cigarette
lighter jack (12V) and has an internal battery. It is VERY handy for
chasing the balloon.

The G4T has a rather poor set of controls that makes it a bit
hard to use. The newer AvMap G5 has a touch screen.